Skin wipe test: A simple, inexpensive, and fast approach in the diagnosis of cystic fibrosis

Objective To assess the performance of a newly developed skin wipe test (SWT) for the diagnosis of cystic fibrosis (CF). Study Design Spontaneously formed sweat from the forearm was wiped by a cotton swab moistened with 100 mu L of deionized (DI) water and extracted into 400 mu L of DI water (SWT). The conventional Macroduct sweat test (ST) was performed simultaneously. SWT samples of 114 CF patients, 76 healthy carriers, and 58 controls were analyzed by capillary electrophoresis with contactless conductivity detection and Cl-/K(+)and (Cl- + Na+)/K(+)ion ratios were evaluated. Chloride concentrations from Macroduct ST were analyzed coulometrically. Results Analysis of 248 SWT samples and simultaneous Macroduct ST samples showed comparable method performance. Two ion ratios, Cl-/K(+)and (Cl- + Na+)/K+, from the SWT samples and Cl(-)values from the ST samples were evaluated to diagnose CF. Sensitivity of the SWT method using the Cl-/K(+)ratio (cutoff value 3.9) was 93.9%, compared to 99.1% when using the (Cl- + Na+)/K(+)ratio (cutoff value 5.0) and 98.3% in using Macroduct Cl-(cutoff value higher or equal to 60 mmol/L). The methods' specificities were 97.8%, 94.0%, and 100.0%, respectively. Conclusions The developed SWT method with capillary electrophoretic analysis for CF diagnosis performs comparably to the conventional Macroduct ST. The SWT method is simple, fast, inexpensive, and completely noninvasive. Use of an ion ratio in obtained SWT samples is proposed as a new diagnostic parameter that shows significant promise in CF diagnostics.